A highly efficient adsorbent adapting to low pH condition for Pb(II) sequestration from aqueous solution − marine diatom: Laboratory and pilot scale tests

Abstract

Highly efficient, economically feasible and environmentally friendly adsorbents have been a research hotspot for heavy metal sequestration. In the present study, dried marine diatom biomass (mainly composed of Chaetoceros sp.), which possessed high suface area and cumulative pore volume of 5.72 m2/g and 0.028 cm3/g, respectivly, were used to adsorb Pb(II) from aqueous solution. The immoblized marine diatom beads and an adsorption reactor filled with the beads were further investigated for continuous Pb(II) removal. The removal efficiency was evaluated as a function of contact time, initial concentration, pH and co-existing cations. Results indicated that the dried diatom biomass and the immobilized diatom beads effectively adsorbed Pb(II) under pH > 3.0 and pH > 4 0.0 conditions, respectively. The optimal conditions for the immobilized diatom beads preparation were: diatom powder dosage of 5.0 g / 100 mL sodium alginate solution, sodium alginate concentration of 20 g/L, CaCl2 concentration of 2 %, and cross linking time of 1 h. The Pb(II) adsorption on the marine diatom biomass and the immobilized beads were both well described by pseudo-second-order kinetic and Langmuir model. The maximumPb(II) adsorption capacities of the immobilized beads were 919.1 mg/g, which were much higher than that of the most of adsorbents reported elsewhere. Adsorption mechanism analysis demonstrated that Pb(II) was adsorbed onto the diatom biomass mainly through interaction with nitrogen bonds (mainly with pyrrolic nitrogen) and carboxylic groups, and ion exchange with light metals and hydrogen ions in quaternary nitrogen bonds. The diatom beads were used as adsorbents in a continuous Pb(II) treatment reactor, and the Pb(II) removal efficiency of the reactor reached to almost 100 % from the initial concentration of Pb(II) = 50 mg/L.